U.S. patent application number 14/712097 was filed with the patent office on 2016-11-17 for synthesis and characterization of a new series of cross-linked (phenol, formaldehyde, alkyldiamine) terpolymers for the removal of toxic metal ions from wastewater.
This patent application is currently assigned to King Fahd University of Petroleum and Minerals. The applicant listed for this patent is King Fahd University of Petroleum and Minerals. Invention is credited to Othman Charles Sadeq AL HAMOUZ.
Application Number | 20160332893 14/712097 |
Document ID | / |
Family ID | 57275988 |
Filed Date | 2016-11-17 |
United States Patent
Application |
20160332893 |
Kind Code |
A1 |
AL HAMOUZ; Othman Charles
Sadeq |
November 17, 2016 |
SYNTHESIS AND CHARACTERIZATION OF A NEW SERIES OF CROSS-LINKED
(PHENOL, FORMALDEHYDE, ALKYLDIAMINE) TERPOLYMERS FOR THE REMOVAL OF
TOXIC METAL IONS FROM WASTEWATER
Abstract
Cross-linked terpolymers made up of phenol, diaminoalkane and
formaldehyde monomeric units. The cross-linked terpolymers are
synthesized via a Mannich mechanism in n-heptane, characterized
with multiple spectroscopic techniques, scanning electron
microscopy and powder X-ray diffraction, and are also investigated
for their Pb.sup.2+ adsorption capacity and thermodynamic
properties. A method of removing Pb.sup.2+ ions from an aqueous
solution or a wastewater sample with these cross-linked terpolymers
is also described.
Inventors: |
AL HAMOUZ; Othman Charles
Sadeq; (Dhahran, SA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
King Fahd University of Petroleum and Minerals |
Dhahran |
|
SA |
|
|
Assignee: |
King Fahd University of Petroleum
and Minerals
Dhahran
SA
|
Family ID: |
57275988 |
Appl. No.: |
14/712097 |
Filed: |
May 14, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J 20/28059 20130101;
B01J 20/264 20130101; C08G 14/06 20130101; C02F 2101/20 20130101;
C02F 1/285 20130101; B01J 20/267 20130101 |
International
Class: |
C02F 1/28 20060101
C02F001/28; B01J 20/26 20060101 B01J020/26; C08G 14/06 20060101
C08G014/06 |
Claims
1: A cross-linked terpolymer comprising polycondensed units of
phenol, diaminoalkane and formaldehyde; wherein the diaminoalkane
has a formula according to Formula 1: ##STR00006## with m,
representing the number of carbon atoms in an alkyl chain, is 4, 6,
8 or 10; and wherein each terminal amino group of the diaminoalkane
unit bridges the aryl group of the phenol unit through a
nitrogen-carbon-aryl linkage.
2: The cross-linked terpolymer of claim 1, wherein the cross-linked
terpolymer has a formula according to Formula 2: ##STR00007##
wherein n, representing the number of repeating units of the
cross-linked terpolymer, is 10 to 10000.
3: The cross-linked terpolymer of claim 1, wherein the phenol,
diaminoalkane and formaldehyde are present in the cross-linked
terpolymer at a molar ratio of 1:2.5-3:y, wherein y.gtoreq.6.
4: The cross-linked terpolymer of claim 1, wherein the
diaminoalkane is at least one substituted and unsubstituted alkane
selected from the group consisting of butane, hexane, octane and
decane.
5: The cross-linked terpolymer of claim 1, further comprising one
or more metal ions coordinated to one or more nitrogen atoms of the
cross-linked terpolymer.
6: The cross-linked terpolymer of claim 1, wherein the cross-linked
terpolymer or a solid material synthesized therefrom has a surface
area of 0.01-0.15 m.sup.2g.sup.-1.
7: The cross-linked terpolymer of claim 1, wherein the cross-linked
terpolymer has an average molecular weight of 1,500-350,000
g/mol.
8: A method of removing Pb.sup.2+ ions from an aqueous solution or
a real wastewater sample, comprising: contacting the aqueous
solution with an adsorbent comprising the cross-linked terpolymer
of claim 1.
9: The method of claim 8, wherein the contacting is carried out at
a temperature of 25-50.degree. C.
10: The method of claim 8, wherein the contacting is carried out at
pH 5-6.
11: The method of claim 8, wherein the contacting is carried out
for 1-5 h.
12: The method of claim 8, wherein the cross-linked terpolymer has
a Pb.sup.2+ adsorption capacity of at least 10 mg L.sup.-1 based on
the total volume of the aqueous solution.
13: The method of claim 8, wherein the cross-linked terpolymer has
a Pb.sup.2+ maximum adsorption capacity of 1-250 mg g.sup.-1 based
on the total weight of the cross-linked terpolymer.
14: The method of claim 8, wherein the contacting removes at least
85% of the Pb.sup.2+ ions present in the aqueous solution.
15: The method of claim 8, wherein after contacting, one or more
Pb.sup.2+ ions are coordinated to one or more nitrogen atoms of the
adsorbent.
16: The method of claim 8, further comprising removing at least one
metal ion selected from the group consisting of Co, Cu, Zn, As, Sr,
Mo, Cd and Hg from the aqueous solution.
17: A method of preparing the cross-linked terpolymer of claim 1,
comprising: polycondensing phenol, diaminoalkane and formaldehyde
to form a terpolymer; and curing the terpolymer to form the
cross-linked terpolymer.
18: The method of claim 17, wherein the polycondensing is carried
out by stirring and heating a mixture comprising the phenol, the
diaminoalkane, the formaldehyde and a reaction medium to
85-95.degree. C.
19: The method of claim 17, wherein the reaction medium is
n-heptane.
20: The method of claim 17, wherein the curing is carried out by
continuously stirring the terpolymer at 85-95.degree. C. for 8-24
h.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] The present invention relates to cross-linked terpolymers.
More particularly, the present invention relates to cross-linked
terpolymers containing polymerized units of phenol, formaldehyde
and alkyldiamine monomers, methods of preparing the terpolymers,
and a method of removing metal ions from an aqueous solution by
adsorbing the metal ions with the terpolymers, which is also used
for treatment of real wastewater samples.
[0003] 2. Description of the Related Art
[0004] The "background" description provided herein is for the
purpose of generally presenting the context of the disclosure. Work
of the presently named inventors, to the extent it is described in
this background section, as well as aspects of the description
which may not otherwise qualify as prior art at the time of filing,
are neither expressly or impliedly admitted as prior art against
the present invention.
[0005] Toxic metal ions, such as lead (Pb.sup.2+) have attracted a
large attention and importance in recent years due to its hazardous
effect on the human health and environment [C. Dulcy Evangelin, S.
G. Gunasekaran, M. Dharmendirakumar, Asia-Pac. J. Chem. Eng. 8
(2013) 189-201; A. Atia, M. Donia, A. M. Yousif, Sep. Purif.
Technol. 61 (2008) 348-357; S. Mahdavi, M. Jalali, A. Afkhami,
Chem. Eng. Commun. 200 (2013) 448-470--each incorporated herein by
reference in its entirety]. The toxicity of lead arises from its
non-biodegradable nature and can accumulate in the human body and
cause hazardous effects, such as, nerve damage, anaemia, retarded
foetal growth. Other effects are seen in children as they absorb
and digest larger amounts of Pb.sup.2+ ions than adults [P. L.
Reagan, E. K. Silbergeld, (1989). Establishing a health based
standard for lead in residential soils. In: Hemphill and Cothern,
eds. Trace substances in environmental health, Supplement to Volume
12, (1990) of Environmental Geochemistry and Health--incorporated
herein by reference in its entirety].
[0006] Several treatment methods have been utilized for the removal
of heavy metal ions such as lead ions from aqueous solutions. Among
these methods, adsorption is considered effective and economical.
The adsorption by cross-linked polymers possesses flexibility in
design and application as the cross-linked polymer can be
functionalized by different chelating groups, regenerated and
reused [A. Jakubiak, I. A. Owsik, B. N. Kolarz, React. Funct.
Polym. 65 (2005) 161-167; B. N. Kolarz, A. Jakubiak, J. Jezierska,
B. Dach, React. Funct. Polym. 68 (2008) 1207-1217; M. R. Maurya, S.
Sikarwar, T. Joseph, P. Manikandan, S. B. Hlligudi, React. Funct.
Polym. 65 (2005) 71-83; K. C. Gupta, A. K. Sutar, Polym. Adv.
Technol. 19 (2008)186-200; K. C. Gupta, A. K. Sutar React. Funct.
Polym. 68 (2008)12-26; M. Ruiz, A. M. Sastre, E. Guibal, React.
Funct. Polym. 45 (2000)155-173; F. Fu, Q. Wang, J. Environ. Manage.
92 (2011) 407-418--each incorporated herein by reference in its
entirety].
[0007] One class of cross-linked polymers is the
phenol-formaldehyde polymer. Phenol-formaldehyde polymers can be
modified to produce ion exchange resins with a variety of
functional groups [F. Lawson and W. H. Jay. Ion exchange resin.
U.S. Pat. No. 6,203,708, assigned to Monash University (Clayton,
AU), Mar. 20 2001--incorporated herein by reference in its
entirety]. Phenol-formaldehyde polymers containing oxime chelating
groups showed high adsorption capacity toward Cu.sup.2+ ion removal
[K. A. K. Ebraheem, S. T. Hamdi, React. Funct. Polym. 34 (1997)
5-10--incorporated herein by reference in its entirety], A
salicylic acid-formaldehyde-catechol terpolymeric resin has been
evaluated for the removal of Ni(II), Cu(II), Zn(II), Pb(II) and
Cd(II) ions [R. R. Bhatt, B. A. Shah, (2013) Arab. J. Chem.,
http://dx.doi.org/10.1016/j.arabjc.2013.03.012 "in
press"--incorporated herein by reference in its entirety], an
anthranilic acid-formaldehyde-2-aminopyridine terpolymer has been
synthesized and evaluated for the removal of Fe(III), Co(II),
Ni(II), Cu(II), Zn(II) and Pb(II) [R. S. Azarudeen, R. Subha, D.
Jeyakumar, A. R. Burkanudeen, Sep. Purif. Technol. 116 (2013)
366-377--incorporated herein by reference in its entirety].
[0008] Polymeric material based on phenol-formaldehyde can be used
in a variety of applications. Such applications include insulation
material, consolidated wood products, oil filters, abrasive
binders, ion exchange membranes and carbon membranes upon
carbonization [F. C. Dupre, M. E. Foucht, W. P. Freese, K. D.
Gabrielson, B. D. Gapud, W. H. Ingram, T. M. McVay, R. A. Rediger,
K. A. Shoemake, K. K. Tutin, J. T. Wright, Cyclic urea-formaldehyde
prepolymer for use in phenolformaldehyde and melamine-formaldehyde
resin-based binders. U.S. Pat. No. 6,379,814, assigned to
Georgia-Pacific Resins, Inc. (Atlanta, Ga.), Apr. 30 2002; K.
Lenghaus, G. G. Qiao, D. H. Solomon, Polymer 42 (2001) 3355-3362;
N. Kishore, S. Sachan, K. N. Rai, A. Kumar, Carbon 41 (2003)
2961-2972--each incorporated herein by reference in its
entirety].
[0009] There is a continuing need in the resin art for resins or
polymers with novel monomers or novel combinations of monomers, to
provide enhanced ion adsorption capacity and/or ion
selectivity.
BRIEF SUMMARY OF THE INVENTION
[0010] According to a first aspect, the present invention relates
to a cross-linked terpolymer comprising polycondensed units of
phenol, diaminoalkane and formaldehyde. The diaminoalkane has a
formula according to Formula 1:
##STR00001##
with m, representing an even number of carbon atoms in an alkyl
chain, is 4, 6, 8 or 10. Each terminal amino group of the
diaminoalkane unit bridges the aryl group of the phenol unit
through a nitrogen-carbon-aryl linkage.
[0011] In one or more embodiments, the cross-linked terpolymer has
a formula according to Formula 2:
##STR00002##
In Formula 2, n, representing the number of repeating units of the
cross-linked terpolymer, is 10 to 10000.
[0012] In one or more embodiments, the phenol, diaminoalkane and
formaldehyde are present in the cross-linked terpolymer at a molar
ratio of 1:2.5-3:y and y.gtoreq.6.
[0013] In one or more embodiments, the diaminoalkane is selected
from the group consisting of substituted and unsubstituted butane,
hexane, octane and decane.
[0014] In one or more embodiments, the cross-linked terpolymer
further comprises one or more metal ions coordinated to one or more
nitrogen atoms of the cross-linked terpolymer.
[0015] In one or more embodiments, the cross-linked terpolymer or a
solid material synthesized therefrom has a surface area of
0.01-0.15 m.sup.2g.sup.-1.
[0016] In one or more embodiments, the cross-linked terpolymer has
an average molecular weight of 1,500-350,000 g/mol.
[0017] According to a second aspect, the present invention relates
to a method of removing Pb.sup.2+ ions from an aqueous solution.
The method comprises contacting the aqueous solution with an
adsorbent comprising the cross-linked terpolymer according to the
first aspect of the invention.
[0018] In one or more embodiments, the contacting is carried out at
a temperature of 25-50.degree. C.
[0019] In one or more embodiments, the contacting is carried out at
pH 5-6.
[0020] In one or more embodiments, the contacting is carried out
for 1-5 h.
[0021] In one or more embodiments, the cross-linked terpolymer has
a Pb.sup.2+ adsorption capacity of at least 10 mg L.sup.-1 based on
the total volume of the aqueous solution.
[0022] In one or more embodiments, the cross-linked terpolymer has
a Pb.sup.2+ maximum adsorption capacity of 1-250 mg g.sup.-1 based
on the total weight of the cross-linked terpolymer.
[0023] In one or more embodiments, the contacting removes at least
85% of the Pb.sup.2+ ions present in the aqueous solution.
[0024] In one or more embodiments, one or more Pb.sup.2+ ions are
coordinated to one or more nitrogen atoms of the adsorbent after
the contacting.
[0025] According to a third aspect, the present invention relates
to a method of preparing the cross-linked terpolymer according to
the first aspect of the invention. The method comprises
polycondensing phenol, diaminoalkane and formaldehyde to form a
terpolymer and curing the terpolymer to form the cross-linked
terpolymer.
[0026] In one or more embodiments, the polycondensing is carried
out by stirring and heating a mixture comprising the phenol, the
diaminoalkane, the formaldehyde and a reaction medium to
85-95.degree. C.
[0027] In one or more embodiments, the reaction medium is
n-heptane.
[0028] In one or more embodiments, the method further comprises
removing at least one metal ion selected from the group consisting
of Co, Cu, Zn, As, Sr, Mo, Cd and Hg from the aqueous solution.
[0029] In one or more embodiments, the curing is carried out by
continuously stirring the terpolymer at 85-95.degree. C. for 8-24
h.
[0030] The foregoing paragraphs have been provided by way of
general introduction, and are not intended to limit the scope of
the following claims. The described embodiments, together with
further advantages, will be best understood by reference to the
following detailed description taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] A more complete appreciation of the disclosure and many of
the attendant advantages thereof will be readily obtained as the
same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0032] FIG. 1 illustrates a process of synthesizing cross-linked
terpolymers according to at least one embodiment of the present
invention.
[0033] FIG. 2 illustrates the Mannich reaction mechanism taking
place during the terpolymer synthesis process of FIG. 1.
[0034] FIG. 3 shows FTIR spectra of cross-linked terpolymers
synthesized according to the process of FIG. 1.
[0035] FIG. 4 shows .sup.13C-NMR spectra of the synthesized
cross-linked terpolymers.
[0036] FIG. 5 shows TGA curves of the synthesized cross-linked
terpolymers.
[0037] FIG. 6 illustrates powder X-ray diffraction patterns for the
synthesized cross-linked terpolymers.
[0038] FIG. 7 illustrates the effect of an aliphatic chain length
chain on the adsorption of Pb.sup.2+ ions by the synthesized
cross-linked terpolymers at pH 5 for 24 h at 25.degree. C.
[0039] FIG. 8 illustrates the effect of pH on structure of the
synthesized cross-linked terpolymers.
[0040] FIG. 9 illustrates the effect of pH on the adsorption
capacity of the synthesized cross-linked terpolymers.
[0041] FIG. 10 A illustrates the effect of Pb.sup.2+ ion solution
concentration on the adsorption capacity of the synthesized
cross-linked terpolymers.
[0042] FIG. 10B shows Langmuir isotherm model plots for Pb.sup.2+
ion adsorption capacity of the synthesized cross-linked
terpolymers.
[0043] FIG. 10C is a Freundlich isotherm model plot for Pb.sup.2+
ion adsorption capacity of the synthesized cross-linked
terpolymers.
[0044] FIG. 10D is a Temkin isotherm model plot for Pb.sup.2+ ion
adsorption capacity of the synthesized cross-linked
terpolymers.
[0045] FIG. 11A illustrates the effect of time at 298, 308 and 323
K on the Pb.sup.2+ ion adsorption capacity of Ph-Buta.
[0046] FIG. 11B is a pseudo first-order kinetic model plot of the
Pb.sup.2+ ion adsorption capacity of Ph-Buta.
[0047] FIG. 11C is a pseudo second-order kinetic model plot of the
Pb.sup.2+ ion adsorption capacity of Ph-Buta.
[0048] FIG. 11D is an intraparticle diffusion model plot of the
Pb.sup.2+ ion adsorption capacity of Ph-Buta.
[0049] FIG. 12A is a SEM-EDX image of unloaded Ph-Buta.
[0050] FIG. 12B is a SEM-EDX image of Ph-Buta loaded with Pb.sup.2+
ions.
[0051] FIG. 12C is a SEM-EDX image of unloaded Ph-Hexa.
[0052] FIG. 12D is a SEM-EDX image of Ph-Buta loaded with Pb.sup.2+
ions.
[0053] FIG. 12E is a SEM-EDX image of unloaded Ph-Octa.
[0054] FIG. 12F is a SEM-EDX image of Ph-Octa loaded with Pb.sup.2+
ions.
[0055] FIG. 12G is a SEM-EDX image of unloaded Ph-Deca.
[0056] FIG. 12H is a SEM-EDX image of Ph-Deca loaded with Pb.sup.2+
ions.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0057] Referring now to the drawings, wherein like reference
numerals designate identical or corresponding parts throughout the
several views.
[0058] The present invention relates to cross-linked terpolymers
having polycondensed phenol, diaminoalkane (or alkyldiamine) and
formaldehyde monomeric units, the diaminoalkane having the
following Formula 1:
##STR00003##
with m=4, 6, 8, 10. Therefore, the diaminoalkane in the
cross-linked terpolymer can be diaminobutane (Buta), diaminohexane
(Hexa), diaminooctane (Octa) or diaminodecane (Dec).
[0059] As can been seen in Formula 1, the alkyl chain of the
alkyldiamine is flanked by two terminal amino groups. The alkyl
chain, selected from the group consisting of butane, hexane, octane
and decane, can be substituted or unsubstituted.
[0060] In certain embodiments, a cross-linked terpolymer according
to the present invention has the following Formula 2:
##STR00004##
where each terminal amino group of the diaminoalkane unit (as
described above) bridges the aryl group of the phenol unit through
a nitrogen-carbon-aryl linkage. In at least one embodiment, three
amino terminated alkyl bridges (from three diaminoalkane units) are
bonded to one central phenol group through a single carbon atom
(e.g., derived from formaldehyde) at the ortho and para positions
of the phenol group. The number of repeating units of a monomer
unit having a single phenolic group is represented by "n" which may
be an integer of from greater than 1 to 10000, preferably from 10
to 5000, 20 to 2500, 25 to 1500, or 100 to 1000.
[0061] In one or more embodiments, phenol, diaminoalkane and
formaldehyde are present in a terpolymer molecule in a molar ratio
of 1:x:y, wherein x=1-5 and y.gtoreq.6. For example, the molar
ratio can be 1:1-5:6-100. In one embodiment, the
phenol:diaminoalkane:formaldehyde molar ratio is 1:3:6.
In some embodiments, the cross-linked terpolymer is selected from
the group consisting of phenol-formaldehyde-diaminobutane
(Ph-Buta), phenol-formaldehyde-diaminohexane (Ph-Hexa),
phenol-formaldehyde-diaminooctane (Ph-Octa) and
phenol-formaldehyde-diaminodecane (Ph-Deca).
[0062] For purposes of the present inventions, "cross-linked" or
"network" or "thermoset" polymers refer to natural or synthetic
polymers and resins that contain branches that connect polymer
chains via covalent bonds. The cross-linking can alter the physical
and mechanical properties of the polymer. The vulcanization of
rubber, for example, results from the introduction of short chains
of sulfur atoms that link the polymer chains in natural rubber. As
the number of cross-links increases, the polymer becomes more
rigid.
[0063] In certain embodiments, the hardness of a terpolymer
according to the present invention can vary from hard to
rubbery-like and flexible, which can be correlated to the length or
number of carbon atoms in the alkyl chain of the diaminoalkane.
Accordingly, the longer the alkyl chain, the more flexible a
terpolymer will be. In some embodiment that alkyl chain may have
more the 10 carbon atoms, e.g., 12, 14, 16, 18 or 20 carbon
atoms.
[0064] In some embodiments, the morphology of a terpolymer
synthesized according to the present invention can vary between
spherical white pellets and a single white, large lump. This is
also correlated to the length or number of carbon atoms in the
alkyl chain of the diaminoalkane. Accordingly, alkyl chains of
.gtoreq.8 carbon atoms (e.g. octane and decane) produce spherical,
white pellets while alkyl chains of <8 carbon atoms (e.g. hexane
and butane) produce single, large lumps.
[0065] The surface area of a cross-linked
phenol-formaldehyde-diaminoalkane terpolymer according to the
present invention or a solid material synthesized therefrom is
within the range of 0.01-0.15 m.sup.2g.sup.-1, preferably 0.02-0.10
m.sup.2g.sup.-1, more preferably 0.02-0.08 m.sup.2g.sup.-1.
[0066] In at least one embodiment, one or more metal ions are
coordinated to one or more nitrogen atoms of the terpolymer. The
metal ions that are coordinated to the terpolymer are preferably
heavy metal ions have a 2+ charge including Pb.sup.2+, Mn.sup.2+,
Fe.sup.2+, Co.sup.2+, Ni.sup.2+, Cu.sup.2+, Sn.sup.2+ and Cd.sup.2+
but may include Be.sup.2+ and/or Zn.sup.2+.
[0067] In at least one embodiment, the metal ions that are
coordinate to the terpolymer include but are not limited to Co, Cu,
Zn, As, Sr, Mo, Cd, Hg and Pb.
[0068] In one or more embodiments, the average molecular weight of
a terpolymer according to the present invention is in the range of
including but not limited to 1,500-350,000 g/mol, 2,500-300,000
g/mol, 3,000-100,000 g/mol, or 5,000-50,000 g/mol.
[0069] In one or more embodiments, a terpolymer composition
comprising the terpolymer exhibits a degree of crystallinity of
70-90%, preferably 73-87%, more preferably 75-85%. The degree of
crystallinity, calculated as (Area under crystalline
peak(2.theta..about.20)/total area under the curve).times.100%, can
be measured by an X-ray diffraction technique such as powder X-ray
diffraction.
[0070] The present invention also relates to methods of preparing
the cross-linked terpolymers described above. In one embodiment,
the polymerization is achieved through polycondensation of phenol,
diaminoalkane and formaldehyde (in a molar ratio of 1:x:y, x=1-5
and y.gtoreq.6, for example 1:1-5:6-100) via a Mannich reaction in
a reaction medium. The reaction medium can be either an aqueous
medium or an organic solvent, such as ethanol, methanol, water,
acetic acid, saturated and unsaturated hydrocarbons such as alkanes
and alkenes. In one embodiment, the reaction medium is
n-heptane.
[0071] For purposes of the present invention, a Mannich reaction
refers to a multi-component condensation of a nonenolizable
aldehyde (e.g. formaldehyde), a primary or secondary amine or
ammonia and an enolizable carbonyl compound to afford an
aminomethylated product, which is also sometimes called a Mannich
base. The Mannich reaction is usually a two-step reaction: addition
of the amine group to the carbonyl carbon of the formaldehyde to
form an electrophilic immonium or iminium ion followed by attack of
the electrophile by the enolizable carbonyl compound.
[0072] Phenol, diaminoalkane and formaldehyde according to the
aforementioned molar ratio are mixed in the reaction medium then
stirred and heated until the temperatures reaches 80-100.degree.
C., preferably 85-95.degree. C., for example, 90.degree. C. A
curing process takes place when the mixture is kept at the reached
maximum temperature for at least 8 h, preferably at least 16 h,
more preferably at least 24 h with continuous stirring. As used
herein, curing refers to the toughening or hardening of a polymer
material by cross-linking of polymer chains, brought about by
agents such as electron beams, heat, chemical additives and UV
radiation. Accordingly, methods of preparing a
phenol-formaldehyde-diaminoalkane cross-linked terpolymer in the
present invention are not limited by the use of heat in the curing
process. Due to a formaldehyde/phenol ratio of >1, the curing
process does not require a cross-linking agent. After the curing
process has been completed, the polymer or resinous material
produced can be filtered, crushed, washed and dried.
[0073] The methods of preparing cross-linked terpolymers described
herein have a product yield of at least 70%, preferably at least
75%, for example, 75-85%. The product yield is calculated as (mass
of product/mass of reactants).times.100%.
[0074] Further, the present invention relates to a method of
removing Pb.sup.2+ ions from an aqueous solution by adsorbing the
Pb.sup.2+ ions with a cross-linked
phenol-formaldehyde-diaminoalkane terpolymer in both batch mode and
fixed-bed or column mode.
[0075] In one or more embodiments, the cross-linked
phenol-formaldehyde-diaminoalkane terpolymer adsorbent is present
in the aqueous solution within a concentration range of 0.1-5.0 g
L.sup.-1 (per volume of the treated aqueous solution), preferably
0.5-2.5 g L.sup.-1, more preferably 1.0-2.0 g L.sup.-1.
[0076] In one or more embodiments, the aqueous solution is within a
pH range of 4-6, preferably 5-6.
[0077] In one or more embodiments, a cross-linked
phenol-formaldehyde-diaminoalkane terpolymer of the present
invention is effective in adsorbing Pb.sup.2+ ions in an aqueous
solution within a temperature of 25-50.degree. C., preferably
35-50.degree. C., more preferably 40-50.degree. C.
[0078] In one or more embodiments, the adsorption of Pb.sup.2+ ions
by a cross-linked phenol-formaldehyde-diaminoalkane terpolymer of
the present invention in an aqueous solution is carried out for a
duration of 1-5 h, preferably 2-5 h, more preferably 3-5 h. More
than 85% of the Pb.sup.2+ ions present in the aqueous solution will
be successfully removed, preferably more than 90%, more preferably
more than 95%, even more preferably more than 99.9%.
Advantageously, more than 70% of the Pb.sup.2+ ions are removed
within the first hour.
[0079] In one or more embodiments, the Pb.sup.2+ adsorption
capacity of a cross-linked phenol-formaldehyde-diaminoalkane
terpolymer increases when the initial concentration of Pb.sup.2+
ions in the aqueous solution increases. The initial concentration
of Pb.sup.2+ ions in the aqueous solution is in the range of 50-136
mg L.sup.-1, preferably 84-136 mg L.sup.-1, more preferably 110-136
mg L.sup.-1.
[0080] In one or more embodiments, the Pb.sup.2+ adsorption
capacity of a cross-linked phenol-formaldehyde-diaminoalkane
terpolymer increases when the number of carbon atoms in the alkyl
chain of diaminoalkane decreases. For example, at pH 5, 25.degree.
C., for a duration of 4 h and at a terpolymer concentration of 1.5
g L.sup.-1, the Pb.sup.2+ adsorption capacities of Ph-Buta,
Ph-Hexa, Ph-Octa and Ph-Deca are 84-88 mg L.sup.-1, 48-52 mg
L.sup.-1, 24-28 mg L.sup.-1 and 12-16 mg L.sup.-1, respectively.
Overall, a cross-linked phenol-formaldehyde-diaminoalkane
terpolymer of the present invention has a Pb.sup.2+ adsorption
capacity of 10-90 mg L.sup.-1 under the described conditions.
[0081] In one or more embodiments, the maximum adsorption capacity
of metal ions on the cross-linked phenol-formaldehyde-diaminoalkane
terpolymer is within the range of 1-250 mg g.sup.-1, preferably
10-250 mg g.sup.-1, more preferably 30-250 mg g.sup.-1.
[0082] In one or more embodiments, the cross-linked
phenol-formaldehyde-diaminoalkane terpolymer adsorbent is also
effective in removing, apart from Pb, other metal ions such as Co,
Cu, Zn, As, Sr, Mo, Cd, and Hg from a wastewater sample.
[0083] The examples below further illustrate protocols for
preparing and characterizing the cross-linked terpolymers described
herein, and are not intended to limit the scope of claims.
Example 1
Materials and Equipment
[0084] Phenol (Ph), paraformaldehyde, 1,4-diaminobutane (Buta),
1,6-diaminohexane (Hexa), 1,8-diaminooctane (Octa) and
1,10-diaminodecane (Deca) from Fluka Chemie AG (Buchs, Switzerland)
were used as received. All solvents used were of analytical
grade.
[0085] Infrared spectra were recorded on a Perkin Elmer 16F PC FTIR
spectrometer using KBr Pellets in the 500-4000 cm.sup.-1 region.
.sup.13C-NMR solid state spectra were recorded on a Bruker WB-400
spectrometer with an operating frequency at 100.61 MHz (9.40 T).
Samples were packed into 4 mm zirconium oxide rotors at 25.degree.
C. Cross-polarization was employed. Pulse delay of 5.0 s and
contact time was 2 ms in CPMAS experiments. Magic angle spinning
rate was 4 KHz. Carbon chemical shifts were referenced to
tetramethylsilane using the high frequency isotropic peak of
adamantine to 38.56 ppm. Scanning electron microscopy (SEM) images
were taken by TESCAN LYRA 3 (Czech Republic) equipped with an
energy-dispersive X-ray spectroscopy (EDX) detector model X-Max.
Atomic absorption spectroscopy (AAS) analysis was performed using
AAS model iCE 3000 series (Thermo Scientific). Thermogravimetric
analysis (TGA) was performed using a thermal analyzer (STA 429) by
Netzsch (Germany). The experiment was performed in a nitrogen
atmosphere from 20-800.degree. C. with a heating rate of 10.degree.
C./min with a nitrogen flow rate of 20 mL/min. X-ray analysis were
performed on Rigaku Rint D/max-2500 diffractometer using Cu
K.alpha. radiation (wave length=1.5418 A) in a scanning range
2.theta.=2-60.degree.. The specific surface area of Ph-Buta was
measured by Burnauer-Emmett-Teller (BET) N.sub.2 method using a
Micro-metrics ASAP 2020 BET surface area analyzer.
Example 2
Synthesis of Cross-Linked Terpolymers
[0086] The cross-linked terpolymers were prepared for the first
time as outlined in FIG. 1, with 0.01 mol of phenol, 0.03 mol of
diaminoalkane and 0.06 mol paraformaldehyde in 30 ml n-heptane as
reaction medium. These reaction components were mixed and stirred
using a magnetic stirrer. When the temperature of the reaction
mixture reached 60.degree. C., a white resinous material was
formed. The heating of the reaction mixture was continued until the
temperature was increased slowly to 90.degree. C. Then, the
reaction mixture was kept at 90.degree. C. for 24 h or overnight
with continuous stirring, and left to cure under such conditions.
Upon completion of reaction the resinous material was filtered,
crushed and left to stir for another 24 h in distilled water. Then,
the product was filtered and washed again with ethanol and dried
under vacuum at 60.degree. C. until constant weight was achieved.
The results obtained are shown in Table 1.
TABLE-US-00001 TABLE 1 Mannich condensation terpolymerization.sup.a
of phenol- formaldehyde-alkyldiamine terpolymers. Elemental
analysis Yield Calculated (%) Observed (%) Terpolymer (%).sup.b C H
N O C H N Ph-Buta 84 66.01 11.08 19.25 3.66 66.52 10.54 18.78
Ph-Hexa 77 69.18 11.61 16.14 3.07 68.76 11.08 16.27 Ph-Octa 78
71.47 12.00 13.89 2.64 71.68 11.80 14.12 Ph-Deca 81 73.20 12.29
12.19 2.32 72.75 12.09 12.33 .sup.aPolymerization reactions were
carried out using 0.01 mol of phenol, 0.03 mol of alkyldiamine and
0.06 mol of paraformaldehyde in 30 ml n-heptane at 90.degree. C.
for 24 h. .sup.bYield (%) = (mass of product/mass of reactants)
.times. 100%.
[0087] The hardness of the synthesized terpolymers varied from hard
to rubbery-like material, which could be explained based on the
length of the aliphatic chain of the diaminoalkane.
1,4-diaminobutane based cross-linked terpolymer showed harder
resin. On the other hand, 1,10-diaminodecane based resin showed
rubbery-like material, the larger amount of alkyl/aromatic ratio
led to more flexible and rubbery like cross-linked terpolymer.
During the synthesis process, the cross-linked terpolymers based on
longer alkyl chains (1,8-diaminooctane and 1,10-diaminodecane)
formed spherical pellets compared with short alkyl chain
(1,4-diaminobutane and 1,6-diaminohexane) that formed one large
lump.
[0088] The synthesis process of the terpolymers proceeded via a
Mannich type reaction mechanism as shown in FIG. 2. At step S210,
the addition of the amine group to the carbonyl carbon of the
formaldehyde formed the immonium ion. At step S220, the immonium
ion was then attacked by the phenol from ortho- and para-positions
by the directing hydroxyl group. The polymer formation depended on
the amount of formaldehyde added: 0.06 mol of formaldehyde was
added (3 times more than diaminoalkane) to allow the reaction to
proceed toward the formation of the cross-linked terpolymers [S. G.
Subramaniapillai, J. Chem. Sci. 125 (2013) 467-482--incorporated
herein by reference in its entirety].
Example 3
Characterization of Terpolymers
[0089] The synthesized terpolymers (Ph-Buta, Ph-Hexa, Ph-Octa and
Ph-Deca) were characterized using a variety of techniques,
including FTIR (Fourier transform infrared) spectroscopy, solid
state .sup.13C-NMR spectroscopy, thermogravimetric analysis TGA)
and powder X-ray diffraction.
[0090] FTIR spectra for the synthesized terpolymers are presented
in FIG. 3. The spectra of the four terpolymers (Ph-Buta, Ph-Hexa,
Ph-Octa and Ph-Deca) are consistent with the proposed structure
given in FIG. 1. The spectra shows a broad band at .about.3425
cm.sup.-1 which is assigned to the intermolecular hydrogen bonding
and the stretching vibration of --OH and --NH groups, respectively
[S. Cavus, G. Gutdag, Ind. Eng. Chem. Res. 48 (2009)
2652-2658--incorporated herein by reference in its entirety]. A
sharp medium band at .about.1613 cm.sup.-1 is assigned to the
Asymmetric --NH bending vibration. Two sharp strong bands at
.about.1595 and .about.1466 cm.sup.-1 are assigned to the C.dbd.C
aromatic ring stretching vibration. The weak sharp band .about.1220
is assigned to C--O stretching vibration. The strong sharp band at
.about.1115 cm.sup.-1 is assigned to C--N stretching vibration. The
band .about.750 is assigned to the N--H wag vibration. The strong
sharp band at .about.720 cm.sup.-1 is assigned to the CH.sub.2 Rock
which indicates a long chain of CH.sub.2 which is consistent with
the long aliphatic chains of the diaminoalkanes, sharp intense
bands at 2925 cm.sup.-1 and 2852 cm.sup.-1 are assigned to C--H
symmetrical and asymmetrical stretching vibrations, were the
intensity of the bands increase with the increase of the aliphatic
chain of the diaminoalkanes [R. S. Azarudeen, R. Subha, D.
Jeyakumar, A. R. Burkanudeen, Sep. Purif. Technol. 116 (2013)
366-377; L. Bellamy, third ed. Infrared Spectra of complex
molecules, chapman and Hall, London, (1975); B. H. Stuart, Infrared
Spectroscopy: Fundamentals and Applications, John Wiley & Sons
Ltd, Chichester, West Sussex (2004)--each incorporated herein by
reference in its entirety].
[0091] Solid state .sup.13C-NMR is considered a powerful technique
for the characterization of cross-linked polymers as they are
insoluble in any solvent [R. Rego, P. J. Adriaensens, R. A.
Carleer, J. M. Gelan, Polymer 45(2004) 33-38; A. Georgakopoulos, J.
Serb. Chem. Soc., 68 (2003) 599-605; I. S. Chuang, G. E. Maciel,
Macromolecules 17 (1984) 1087-1090--each incorporated herein by
reference in its entirety]. The .sup.13C-NMR spectra are shown in
FIG. 4, wherein similar peaks are found to represent the structure
of the four synthesized cross-linked terpolymers and the assignment
of peaks are tabulated in Table 2, but a difference in the
intensity of aliphatic methylene chain (without the methylene units
attached to the amino group) of the diaminoalkane; as the number of
methylene units increase the intensity of the peak .about.30 ppm
increases. The .sup.13C-NMR spectra confirm the structure of the
proposed synthesized cross-linked terpolymers.
TABLE-US-00002 TABLE 2 .sup.13C NMR Data for the synthesized
cross-linked terpolymers. ~.delta. (ppm) Structure* 1 2 3 4 5 6
##STR00005## 167 133 95 80 55 30 *The structure is part of the
terpolymer, all unassigned carbons have similar peaks.
[0092] The elemental analysis data of the synthesized terpolymers
in Table 1 was in good agreement with the proposed structure. As
the chain length increases the structure is added with three
CH.sub.2 units increasing the % of carbon and decreasing the % of
nitrogen in the polymer monomer unit.
[0093] Thermogravimetric analysis (TGA) was carried out in order to
evaluate the thermal stability of the synthesized terpolymers and
the TGA curves are shown in FIG. 5. The Ph-Buta thermogram shows
three major degradation patterns: initial .about.16% at
72-236.degree. C. due to the loss of water molecules strongly held
within the terpolymer network by intermolecular hydrogen bonds
which indicates the high hydrophilicity of Ph-Buta, then a sharp
weight loss of .about.38% at 236-353.degree. C. due to the thermal
degradation of the aliphatic chain of 1,4-diaminobutane, finally, a
gradual weight loss of .about.25% at 353-800.degree. C. due to
carbonization or pyrolysis of the aromatic moieties [I. Muylaert,
A. Verberckmoes, J. De Decker, P. Van Der Voort, Adv. Colloid
Interfac. 175 (2012) 39-51--incorporated herein by reference in its
entirety]. The Ph-Hexa, Ph-Octa and Ph-Deca thermograms show
similar trends of thermal degradation. Water loss in the
thermograms is absent and this could be explained by the higher
ratio of hydrophobic to hydrophilic character found in the longer
aliphatic chains, which expels water molecules out the polymer
matrix. The Ph-Hexa, Ph-Octa and Ph-Deca thermograms in FIG. 5,
show two major degradation patterns. The first degradations include
a weight loss of .about.50% at 141-296.degree. C. for Ph-Hexa,
.about.50% at 160-279.degree. C. for Ph-Octa and .about.60% at
164-430.degree. C. for Ph-Deca due to the loss of the aliphatic
chains of diaminoalkane. The higher thermal stability possessed by
Ph-Deca, may be due the higher van der Waals interaction that
increases with increasing the chain length [A. R. Hirst, D. K.
Smith, M. C. Feiters, H. P. M. Geurts, Langmuir 20 (2004)
7070-7077--incorporated herein by reference in its entirety]. The
second degradations include .about.41% weight loss at
296-800.degree. C. for Ph-hexa, .about.42% at 279-800.degree. C.
for Ph-Octa and .about.37% at 430-800.degree. C. for Ph-Deca, all
of which could be due to carbonization and pyrolysis [I. Muylaert,
A. Verberckmoes, J. De Decker, P. Van Der Voort, Adv. Colloid
Interfac. 175 (2012) 39-51--incorporated herein by reference in its
entirety].
[0094] Powder X-ray diffraction (XRD) patterns shown in FIG. 6
reveal the presence of a peak at 2.theta..about.20.degree.; an
increase of the chain length of the diaminoalkane present in the
terpolymer showed enhanced crystallinity of the synthesized
terpolymers. Upon calculating the degree of crystallinity (Table 3)
the highest degree of crystallinity was for Ph-Deca (83.1%). A
possible explanation for this observation was that the formation of
the terpolymers happened within a short time of the reaction
process, then the terpolymers were left to cure at 90.degree. C.
for 24 h allowing the terpolymer chains to reorder and longer
chains with higher flexibility showed enhanced crystallinity [J.
Blackwell, M. R. Nagarajan, T. B. Hoitink, Polymer 23 (1982)
950-956--incorporated herein by reference in its entirety].
TABLE-US-00003 TABLE 3 Degree of crystallinity of the synthesized
cross-linked terpolymers upon the XRD diagram shown in FIG. 6.
Cross-linked terpolymer Degree of crystallinity (%)* Ph-Buta 79.7
Ph-Hexa 81.4 Ph-Octa 82.7 Ph-Deca 83.1 *Degree of crystallinity =
(Area under crystalline peak(2.theta.~20)/total area under the
curve) .times. 100%.
Example 4
Adsorption Experiments
[0095] Adsorption experiments of the synthesized cross-linked
terpolymers for Pb.sup.2+ ions were performed in a similar fashion
as previously reported [S. A. Ali, O. C. S. Al-Hamouz, N. M.
Hassan, J. Hazard. Mater. 248-249 (2013) 47-58--incorporated herein
by reference in its entirety]. Accordingly, 0.03 g of terpolymer,
powder or pellet form, was mixed with 20 ml of a Pb(NO.sub.3).sub.2
solution of a desired pH and stirred for 24 h. The
Pb(NO.sub.3).sub.2-terpolymer mixture was filtered and washed with
deionized water. The amount of Pb.sup.2+ ions in the filtrate was
analyzed by Atomic absorption spectroscopy (AAS). The adsorption
capacity (q.sub.e) in mg g.sup.-1 can be found by the following
Equation 1:
q e = ( C o - C f ) V W ( Equation 1 ) ##EQU00001##
where C.sub.o and C.sub.f are initial and final concentration of
Pb.sup.2+ ions in mg L.sup.-1, respectively, W is the weight of the
dried terpolymer in g, and V is the volume of solution in L. The
results obtained represent the average of three runs and varied by
less than 5%. The adsorption isotherms were carried out by changing
the concentration of Pb.sup.2+ ions from 50-135 mg L.sup.-1 at pH 5
for 4 h at 25.degree. C. For adsorption kinetics, Ph-Buta was
immersed in 20 ml of 136 mg L.sup.-1 solution of Pb.sup.2+ ions for
different durations at pH 5.
[0096] Two main functionalities are responsible for the adsorption
of Pb.sup.2+ ions in the synthesized cross-linked terpolymers; the
hydroxyl group (--OH) and the secondary amine group (--NH--). The
presence of two lone pairs on the oxygen atom and one lone pair on
the nitrogen atom with high electronegativity (oxygen=3.5 and
nitrogen=3.0) provide high electrostatic attraction between the
positive Pb.sup.2+ ions and the synthesized cross-linked
terpolymers. Another factor is the length of the diaminoalkane
chain; where 25 mg of each cross-linked terpolymer was immersed in
20 ml of 136 mg L.sup.-1 solution of Pb.sup.2+ ions and stirred for
24 h, filtered and the concentration of the solution was measured
before and after adsorption. As seen in FIG. 7, as the chain length
of the diaminoalkane increases the adsorption capacity decreases
which could be attributed repulsion between the long hydrophobic
entangled methylene chains (--(CH.sub.2).sub.n--) with Pb.sup.2+
hydrophilic hydration shell.
Example 5
Effect of pH on Adsorption Capacity of Terpolymers
[0097] The effect of pH is an important factor in the adsorption of
heavy metals as H.sup.+ is competing for the adsorption sites in
the synthesized cross-linked terpolymers. The second factor is
metal speciation where, upon reaching a pH of 6 and above lead ions
precipitate forming lead hydroxide precipitates [A. A. Mengistie,
T. S. Rao, A. V. Rao, M. Singanan, Bull. Chem. Soc. Ethiop. 22
(2008) 349-360; P. X. Sheng, Y. P. Ting, J. P. Chen, L. Hong, J.
Colloid Interface Sci. 275(2004) 131-141; H. B. Bradl, J. Colloid
Interface Sci. 277 (2004) 1-18; M. Machida, R. Yamazaki, M. Aikawa,
H. Tatsumoto, Sep. Purif. Technol. 46 (2005) 88-94--each
incorporated herein by reference in its entirety].
[0098] As can be seen in FIG. 8, at low pH values, the positive
ammonium ion (--.sup.+NH.sub.2--) predominates leading to
electrostatic repulsion with positive Pb.sup.2+ ions. No effect on
the hydroxyl (--OH) group within the pH range of 2-6 as
deprotonation will not occur until pH.about.8 [D. D. O. Vaz, A. N.
Fernandes, B. Szpoganicz, M. M. Sierra, Eclet. Quim. 35 (2010)
147-152--incorporated herein by reference in its entirety]. On the
contrary, a higher pH decreases the amount of positive H.sup.+ and
increases the negative charge on the surface of the cross-linked
terpolymer leading to higher electrostatic attraction with
Pb.sup.2+ ions. The effect of pH on the adsorption capacity is
shown in FIG. 9. As the pH increases the adsorption capacity
increases.
Example 6
Effect of Initial Concentration on Pb.sup.2+ Adsorption Capacity of
Terpolymers
[0099] The effect of initial concentration was studied at pH=5 on
solutions of Pb.sup.2+ ions with an initial concentration C.sub.o
ranging between 55 and 136 mg L.sup.-1. The effect of initial
concentration on the adsorption capacities of the synthesized
cross-linked terpolymers are shown in FIG. 10A. FIG. 10A shows that
the adsorption capacity increases with an increase of initial
concentration. To further explore the adsorption mechanism, three
isotherm models were employed; Langmuir, Freundlich and Temkin
isotherm models in order to investigate the adsorption data which
is shown in Table 4.
[0100] The Langmuir model is utilized to describe the adsorption of
an adsorbate on a homogeneous surface of an adsorbent, where each
adsorption site can be occupied by one metal ion and there is no
interaction between the adsorbed metal ions. FIG. 7A and Table 4
show that the adsorption data fits well with the Langmuir model.
The linear form of the Langmuir model can be expressed by the
following Equation 2 [R. S. Azarudeen, R. Subha, D. Jeyakumar, A.
R. Burkanudeen, Sep. Purif. Technol. 116 (2013) 366-377; Y. Zhu, J.
Hu, J. Wang, J. Hazard. Mater. 221-222 (2012) 155-61; P.
Kampalanonwat, P. Supaphol, ACS Appl. Mater. Interfaces. 2 (2010)
3619-27--each incorporated herein by reference in its
entirety]:
C e q w = C e Q m + 1 Q m b ( Equation 2 ) ##EQU00002##
where q.sub.e and C.sub.e are the adsorption capacity at
equilibrium (mg g.sup.-1) and concentration of metal ions at
equilibrium (mg L.sup.-1), respectively, Q.sub.m is the maximum
adsorption capacity of metal ions on the adsorbent (mg g.sup.-1)
and b is the Langmuir constant related to the adsorption energy (L
mg.sup.-1). The values of Q.sub.m and b are found in Table 4. As
can be seen from Table 4 and FIGS. 11A-11D, Q.sub.m values decrease
as the methylene chain length of the diaminoalkane increase,
indicating higher accessibility to adsorption sites in Ph-Buta
compared to Ph-Deca. A higher amount of aliphatic hydrophobic
chains leads to lower adsorption capacity as a higher amount of
hydrophobic moiety masks the adsorption sites from hydrophilic
hydration shell of Pb.sup.2+ ions. A smaller length of aliphatic
chains increases the concentration of the adsorption sites by
exposing the adsorption sites to Pb.sup.2+ ions which increases the
adsorption capacity.
TABLE-US-00004 TABLE 4 Langmuir, Freundlich and Temkin isotherm
model constants for Pb.sup.2+ ion adsorption. Freundlich isotherm
model Cross- Langmuir isotherm model k.sub.f Temkin isotherm model
linked Q.sub.m b (mg.sup.1-1/n g.sup.-1 A B terpolymer (mg
g.sup.-1) (L mg.sup.-1) R.sup.2 L.sup.1/n) n R.sup.2 (L g.sup.-1)
(J mol.sup.-1) R.sup.2 Ph-Buta 222.2 0.0044 0.9728 0.800 1 1 0.0362
62.40 0.9891 Ph-Hexa 33.33 0.0311 0.9668 0.800 1 1 0.0597 37.26
0.9939 Ph-Octa 10.40 0.0406 0.9604 0.800 1 1 0.1211 18.47 0.9931
Ph-Deca 1.425 -3.003 0.9442 0.800 1 1 0.2137 10.31 0.9950
[0101] A dimensionless factor or equilibrium parameter (R.sub.L)
which can be utilized to show the favorability of adsorption on the
terpolymer surface by Equation 3:
R L = 1 ( 1 + bC o ) ( Equation 3 ) ##EQU00003##
where C.sub.o is the initial metal concentration of Pb.sup.2+ ions
(mg L.sup.-1) and b is the Langmuir constant. If the value of
R.sub.L falls in the region of 0<R.sub.L<1; the adsorption is
favorable, if R.sub.L=0 then the adsorption is irreversible. As
shown in Table 5, all the values are found between
0<R.sub.L<1 which indicate favorable adsorption occurring on
the synthesized cross-linked terpolymers, except, Ph-Deca. The
values of R.sub.L.apprxeq.0, which indicates irreversible
adsorption, could be explained by the entrapment of adsorbed
Pb.sup.2+ ions inside the cross-linked terpolymers by long
entangled chains. The R.sub.L values decreased by increasing the
initial concentration of Pb.sup.2+ ions which indicates that the
adsorption process is more favorable at higher concentration of
Pb.sup.2+ ions (Table 5) [A. F. Shaaban, D. A. Fadel, A. A.
Mahmoud, M. A. Elkomy, S. M. Elbahy, J. Environ. Chem. Eng. 2
(2014) 632-641--incorporated herein by reference in its entirety].
High % removal was observed as shown in Table 6, where a .about.98%
removal was achieved by Ph-Buta at an initial concentration of 55
mg L.sup.-1. The high % removal indicates the potential use of the
synthesized cross-linked terpolymers in the removal of toxic metal
ions from wastewater.
TABLE-US-00005 TABLE 5 The R.sub.L values based on the Langmuir
isotherm model. Ph-Buta Ph-Hexa Ph-Octa Ph-Deca C.sub.o % % % % (mg
L.sup.-1) R.sub.L Removal R.sub.L Removal R.sub.L Removal R.sub.L
Removal 55 0.8052 98.18 0.3689 63.63 0.3096 30.87 -0.006 18.68 84
0.7301 92.94 0.2768 52.54 0.2269 27.38 -0.004 14.66 110 0.6736
86.94 0.2261 49.04 0.1831 25.45 -0.003 12.54 136 0.6256 81.62
0.1912 44.85 0.1534 22.79 -0.003 11.76
TABLE-US-00006 TABLE 6 First-order, second-order and Intraparticle
diffusion kinetic models constants. Pseudo first-order Pseudo
second-order Intraparticle diffusion model Temperature q.sub.e, exp
q.sub.e, cal k.sub.1 q.sub.e, cal k.sub.2 h.sup.a k.sub.i (K) (mg
g.sup.-1) (mg g.sup.-1) (h.sup.-1) R.sup.2 (mg g.sup.-1) (g
mg.sup.-1h.sup.-1) (mg g.sup.-1h.sup.-1) R.sup.2 (mg
g.sup.-1h.sup.0.5) C R.sup.2 298 92 42 0.6743 0.9723 94 0.0590
525.0 0.9984 51.74 30.79 0.9952 308 96 44 0.8231 0.9150 97 0.0624
588.2 0.9980 71.81 20.96 0.9808 323 98 42 0.7713 0.9385 100 0.0625
625.0 0.9988 77.81 20.56 0.9779 .sup.ah = k.sub.2q.sub.e.sup.2
(initial rate of adsorption)
[0102] The Freundlich model is utilized to describe the adsorption
of an adsorbate on a heterogeneous surface with uniform energy of
an adsorbent. The linear form of the freundlich model can be
expressed by the following Equation 4 [S. Khalili, A. A. Ghoreyshi,
M. Jahanshahi, K. Pirzadeh, CLEAN--Soil Air Water 41 (2013)
939-948; T. Tay, M. Candan, M. Erdem, Y. Ciimen, H. Turk,
Clean--Soil Air Water 37 (2009) 249-255; C. L. Hsueh, Y. W. Lu, C.
C. Hung, Y. H. Huang, C. Y. Chen, Dyes Pigm. 75 (2007)
130-135--each incorporated herein by reference in its
entirety]:
log q e = log k F + 1 n log C e ( Equation 4 ) ##EQU00004##
where k.sub.f and 1/n are constants related to adsorption capacity
and intensity of adsorption [H. K. Boparai, M. Joseph, D. M.
O'Carroll, J. Hazard. Mater. 186 (2011) 458-465--incorporated
herein by reference in its entirety]. As shown in FIG. 10C, the
data fitted the model, as all the data for different terpolymers
showed similar fitness to the model which could be due to similar
functional groups found in the cross-linked terpolymers. The
results showed that the adsorption process is considered to be
heterogeneous in nature as the correlation coefficient (R.sup.2) of
the data is unity.
[0103] The Temkin isotherm model postulates that the adsorption
energy decreases linearly with the increase in surface coverage
with metal ions due to adsorbent-adsorbate interactions, and the
adsorption process is described by the uniform distribution of
binding energies up to a maximum [A. F. Shaaban, D. A. Fadel, A. A.
Mahmoud, M. A. Elkomy, S. M. Elbahy, J. Environ. Chem. Eng. 2
(2014) 632-641; 42]. The linear form of the Temkin isotherm model
can be described as:
q e = Rt b ln A + Rt b ln C e ( Equation 5 ) q e = B ln A + B ln C
e ( Equation 6 ) ##EQU00005##
where R is gas constant (8.314 J mol.sup.-1 K.sup.-1), t is
temperature (K), A is the equilibrium binding constant (L g.sup.-1)
corresponding to the maximum binding energy, and constant B=Rt/b is
related to the heat of adsorption(J mol.sup.-1). A plot of q.sub.e
versus lnC.sub.e (FIG. 10D) is used to calculate the Temkin
isotherm constants A and B. linear plots with correlation
coefficients >0.99 (Table 4) supports that the adsorption
process of Pb.sup.2+ ions on the synthesized cross-linked
terpolymers to be considered as a chemisorption process [H. K.
Boparai, M. Joseph, D. M. O'Carroll, J. Hazard. Mater. 186 (2011)
458-465--incorporated herein by reference in its entirety].
Example 7
Effect of Time and Temperature on Pb.sup.2+ Adsorption Capacity of
Terpolymers
[0104] Time is an important factor for determining the adsorption
mechanism by determining the rate-limiting step of the adsorption
process. The time was restricted to no more than 4 h, where longer
periods of time resulted in 100% removal of lead ions. Another
factor is temperature were the thermodynamics of the adsorption
process could be determined, three temperatures were studied at
298, 308 and 323 K at C.sub.o=136 mg L.sup.-1, an increase in the
adsorption capacity as the temperature increased which could be
explained by the increased swelling and expansion by the increase
in temperature allowing more Pb.sup.2+ ions to diffuse through and
hence increase the adsorption capacity. Also, the increase in
adsorption capacity with the increase in temperature suggests that
the adsorption process is endothermic in nature (FIG. 11A). The
mechanism of adsorption and thermodynamics will be determined for
Ph-Buta as found to be the most efficient adsorbent in removing
Pb.sup.2+ ions for aqueous solution.
[0105] To evaluate the kinetics and mechanism of the adsorption
process, the pseudo first-order, second-order and the intraparticle
diffusion models were tested to explain the experimental data which
is represented in Table 6. These models are important in order to
design new adsorbents for the treatment of water and waste water
resources [R. S. Azarudeen, R. Subha, D. Jeyakumar, A. R.
Burkanudeen, Sep. Purif. Technol. 116 (2013) 366-377; R. Subha, C.
Namasivayam, Can. J. Civil Eng. 36 (2009) 148-159--each
incorporated herein by reference in its entirety].
[0106] Pseudo first-order kinetic model of the lageregren model
describes the adsorption in solid-liquid systems and assumes that
one metal ion is adsorbed on one site on the adsorbent surface. The
linear form of the model can be represented by the following
Equation 7 [Z.-Y. He, H.-L. Nie, C. Branford-White, L.-M. Zhu,
Y.-T. Zhou, Y. Zheng, Bioresour. Technol. 99 (2008)
7954-7958--incorporated herein by reference in its entirety]:
log ( q e - q t ) = log q e - k 1 2.303 t ( Equation 7 )
##EQU00006##
where q.sub.e and q.sub.t are the adsorption capacity at
equilibrium and at time t (mg g.sup.-1), respectively. k.sub.1 is
the first-order rate constant of adsorption (h.sup.-1). The values
of k.sub.1 and q.sub.e can be calculated from the slope and
intercept of the plot in FIG. 11B (Table 6). the correlation
coefficient of the plots in FIG. 11B are relatively good however
the values of q.sub.e are not in agreement with the experimental
values represented in Table 6, Which suggests that the adsorption
of Pb.sup.2+ ions on Ph-Buta did not follow the pseudo first-order
kinetic model.
[0107] Pseudo second-order kinetic model which is based on
equilibrium adsorption and has been utilized for analyzing
chemisorption kinetics from aqueous solutions can be linearly
represented by the following Equation 8 [X. Ma, L. Li, L. Yang, C.
Su, K. Wang, S. Yuan, J. Hazard. Mater. 209-210 (2012)
467-77--incorporated herein by reference in its entirety]:
t q t = 1 k 2 q e 2 + 1 q e t ( Equation 8 ) ##EQU00007##
where k.sub.2 and q.sub.e are the pseudo second-order rate constant
(g mg.sup.-1h.sup.-1) and the adsorption capacity at equilibrium,
respectively, which are calculated from the slope and intercept of
the plot in FIG. 11C. The values of q.sub.e and k.sub.2 are
presented in Table 6, and the correlation coefficients show that
the adsorption process follows the kinetic model with adsorption
capacities that agree with the experimental data. Another factor
that should be noticed is the rate constant which increases as the
temperature increase, suggesting that the adsorption process is
endothermic. The fitness of the data with the kinetic model
suggests that the adsorption process is chemisorption. Also the low
surface area of Ph-Buta=0.0219 m.sup.2g.sup.-1 also agrees with the
second-order kinetic model that the adsorption process is
chemisorption.
[0108] The intraparticle diffusion model which is used to
investigate the mechanism of adsorption for a solid-liquid
adsorption process can be described by three steps [H. K. Boparai,
M. Joseph, D. M. O'Carroll, J. Hazard. Mater. 186 (2011) 458-465;
E. I. Unuabonah, K. O. Adebowale, B. I. Olu-Owaolabi, J. Hazard.
Mater. 144 (2007) 386-395--each incorporated herein by reference in
its entirety]: [0109] i. Transfer of metal ions from the bulk
solution through liquid film to the adsorbent external surface
(film diffusion). [0110] ii. Intraparticle diffusion, where the
metal ions diffuse through the external surface into the pores of
the adsorbent. [0111] iii. Adsorption on the interior surface of
the adsorbent.
[0112] The final step is considered rapid and is negligible as the
adsorption process comes to equilibrium. To identify the mechanism
controlling the adsorption mechanism, Weber and Morris
intraparticle diffusion model was used in order to determine
whether the rate-limiting step is controlled by film diffusion or
intraparticle diffusion and can be described using the following
Equation 9:
q.sub.t=k.sub.it.sup.0.5+C (Equation 9)
where q.sub.t is the adsorption capacity at time t, K.sub.i is the
rate constant of intraparticle diffusion, C is related to boundary
layer thickness. In order for the adsorption process to be totally
controlled by the intraparticle diffusion model, a plot of q.sub.t
versus t.sup.0.5 has to fit the model and pass through the origin.
But it has been reported that the plot of q.sub.t versus t.sup.0.5
is multilinear and the adsorption process proceeds via multiple
steps [H. K. Boparai, M. Joseph, D. M. O'Carroll, J. Hazard. Mater.
186 (2011) 458-465; E. I. Unuabonah, K. O. Adebowale, B. I.
Olu-Owaolabi, J. Hazard. Mater. 144 (2007) 386-395--each
incorporated herein by reference in its entirety].
[0113] The adsorption process of Pb.sup.2+ ions by Ph-Buta (FIG.
11D) showed three linear steps: first, rapid adsorption that
represents film diffusion, the second linear step shows gradual
increase in the adsorption capacity representing the rate-limiting
step by intraparticle diffusion (Table 6), and finally, the third
linear step which is achieving equilibrium. As shown in FIG. 11D,
the plot did not pass through the origin indicating that
intraparticle diffusion is not the only rate determining step. As
shown in Table 6 the intercept values decreased as the temperature
increased which could be attributed to the decrease in thickness of
the boundary layer surrounding the adsorbent, suggesting that film
diffusion becomes less effective in the rate determining step [E.
I. Unuabonah, K. O. Adebowale, B. I. Olu-Owaolabi, J. Hazard.
Mater. 144 (2007) 386-395; F. C. Wu, R. L. Tseng, R. S. Juang,
Chem. Eng. J. 153 (2009) 1-8--each incorporated herein by reference
in its entirety].
Example 8
SEM-EDX Images of Unloaded and Pb.sup.2+-Loaded Terpolymers
[0114] Unloaded and Pb.sup.2+-loaded terpolymers were analyzed by
scanning electron microscopy. The terpolymers were first immersed
in 125 mg L.sup.-1 Pb.sup.2+ ion solution for 24 h at room
temperature, filtered and dried. Loaded and unloaded terpolymers
were then coated with a thin film of gold. SEM-EDX images reveal
that the adsorption of Pb.sup.2+ ions has occurred on the surface
and throughout the terpolymers as shown in FIGS. 12A-12H.
Example 9
Treatment of Wastewater Samples with pH-Buta
[0115] In order to investigate the effectiveness of Ph-Buta, two
wastewater samples were used. 0.03 g of Ph-Buta was immersed in 20
ml spiked and unspiked wastewater samples and left to stir for 24
hours. The polymer was filtered and washed with distilled water and
the filtrate was analyzed. The metal concentration before and after
adsorption was analyzed via ICP-MS. The results before and after
adsorption with Ph-Buta are shown in Tables 7 and 8. The results
show high efficacy in the removal of lead, cadmium, zinc and copper
metal ions from wastewater samples. Ph-Buta showed 100% removal of
lead (II) ions from the spiked wastewater sample indicating high
potential as an efficient adsorbent for the removal of toxic metal
ions from wastewater samples.
TABLE-US-00007 TABLE 7 Comparison of metals concentration in a
spiked wastewater sample 1 obtained from a water treatment plant
(Doha, Saudi Arabia). Original After Treatment with Ph-Buta Metal
Sample (.mu.g L.sup.-1) (.mu.g L.sup.-1) Co 1.118 .+-. 0.291 0.47
.+-. 0.096 Cu 949.1 .+-. 49.14 200.8 .+-. 0.685 Zn 749.20 .+-. 58.5
46.25 .+-. 9.63 As 5.455 .+-. 0.447 4.815 .+-. 0.67 Sr 4677.0 .+-.
387.0 4258.0 .+-. 61.30 Mo 6.272 .+-. 0.318 11.6 .+-. 0.18 Cd 0.787
.+-. 0.285 <MDL Hg 9.436 .+-. 0.386 1.075 .+-. 0.18 Pb <MDL
<MDL Mean and standard deviation of triplicates (n = 3).
.+-.Values are the detection limit (MDL), 3.sigma. of blank
sample.
TABLE-US-00008 TABLE 8 Comparison of metals concentration in a
spiked wastewater sample 2 obtained from a water treatment plant
(Doha, Saudi Arabia). Original After Treatment with Ph-Buta Metal
Sample (.mu.g L.sup.-1) (.mu.g L.sup.-1) Co 1.118 .+-. 0.291 0.548
.+-. 0.291 Cu 949.1 .+-. 49.14 153.2 .+-. 49.14 Zn 749.20 .+-. 58.5
67.82 .+-. 58.5 As 5.455 .+-. 0.447 4.607 .+-. 0.447 Sr 4677.0 .+-.
387.0 4288.0 .+-. 387.0 Mo 6.272 .+-. 0.318 7.01 .+-. 0.318 Cd
0.787 .+-. 0.285 <MDL Hg 9.436 .+-. 0.386 1.32 .+-. 0.386 Pb
(spiked) 1052.0 .+-. 12.01 <MDL Mean and standard deviation of
triplicates (n = 3). .+-.Values are the detection limit (MDL),
3.sigma. of blank sample.
[0116] Thus, the foregoing discussion discloses and describes
merely exemplary embodiments of the present invention. As will be
understood by those skilled in the art, the present invention may
be embodied in other specific forms without departing from the
spirit or essential characteristics thereof. Accordingly, the
disclosure of the present invention is intended to be illustrative,
but not limiting of the scope of the invention, as well as other
claims. The disclosure, including any readily discernible variants
of the teachings herein, defines, in part, the scope of the
foregoing claim terminology such that no inventive subject matter
is dedicated to the public.
* * * * *
References